Portable electronic devices, such as smartphones and tablets are popular with consumers. Such portable electronic devices are capable of audio playback, and thus employ audio amplifiers. Since these portable electronic devices are powered by batteries, reduction of power consumption is a commercial desire, and thus class D audio amplifiers, which are more efficient than class AB audio amplifiers, may potentially be useful for incorporation into these electronic devices.
A class D amplifier is an electronic amplifier in which the amplifying devices (typically MOSFETs) operate as electronic switches, instead of as linear gain devices as in other amplifiers. The analog signal to be amplified is converted to a series of square pulses before being applied to the amplifying devices. Since the signal to be amplified is a train of constant amplitude pulses, the amplifying devices switch rapidly back and forth between conductive and nonconductive states. After amplification, the output pulse train can be converted back to an analog signal by passing it through a passive low pass filter.
As stated, an advantage of a class D amplifier is that it can be more efficient than other amplifiers, since less power is dissipated as heat in the active devices. However, the switching of the active devices results in increased EMI, which is particularly undesirable in smartphones and tablets. As such, improved class D amplifier designs which reduce EMI are commercially desirable.